Pipe leak detection

ABSTRACT

A pipe leak testing arrangement which includes a device having sealing bags joined by a coupling. When inflated, the bags form a seal volume chamber. The bags may not form a perfect seal, and as a result leakage past the bags may occur when a differential pressure is present. A remaining portion of the pipe forms a test volume chamber. A first transducer measures differential pressure between the chambers and a further transducer measures the test chamber pressure. Measured pressure information is used by a control device to track pressure change and to adjust the seal pressure so as to maintain equal pressures even if the test pressure decays due to a pipe fracture. In an alternative arrangement, two separate devices with associated circuitry are provided to facilitate two temporary seal pressure chambers with the test chamber therebetween.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to measuring leakage through ducts, typicallyfluid carrying pipes.

2. Discussion of the Background

In fluid carrying pipes such as gas mains, for, example, it has beennecessary to isolate sections of main carrying the gas by cut out andbypass techniques and then capping-off. This is time consuming andcostly. With service pipes it is again disruptive to determine leaks.

SUMMARY OF THE INVENTION

The present invention is concerned with providing a less disruptive andless expensive mechanism to provide an accurate pressure leakage test ofpipes.

According to the invention there is provided a leak testing system forpipes including means for providing a temporary seal at a firstlocation;

means for providing a substantially equal pressure between the firstlocation and an adjacent test location to prevent fluid passagetherebetween;

means for determining any pressure decay at the test location indicativeof pipe leakage; and

means for adjusting the pressure in the first location to track anypressure decay in the test location so as to maintain the substantiallyequal pressure between the first and test locations during testing.

Further according to the invention there is provided a method fortesting leaks in pipes and comprising:

providing a temporary seal at a first location;

providing a substantially equal pressure between the first location andan adjacent test location to prevent fluid passage therebetween;

determining any pressure decay at the test location indicative of pipeleakage; and

adjusting the pressure in the first location to track any pressure decayin the test location so as to maintain the substantially equal pressurebetween the first and test locations during testing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference tothe accompanying drawings in which:

FIG. 1 shows a first embodiment of the invention;

FIG. 2 shows a more detailed arrangement;

FIG. 3 shows a schematic diagram for tracking control;

FIG. 4 shows a further arrangement showing two test assemblies; and

FIG. 5 illustrates an alternative configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The arrangement of FIG. 1 is configured to provide two seal volumes witha virtual seal therebetween. A pipe 10, typically carrying a fluid underpressure, e.g. natural gas, is shown sealed at one end 11. This seal maybe permanent or merely temporary to allow the test apparatus to beutilized.

The leakage test device 12 includes a first seal member 14 and a secondmember 15 joined by coupling 16. The seal members 14 and 15 can beinflatable bags which when inflated form a seal with the pipe so as todefine a seal volume chamber 18. The bag seals may, in practice, beimperfect and have the potential of leakage past them. The configurationdescribed below accommodates such a leaky seal. The remaining portion ofthe pipe towards the sealed end 11 forms a test volume chamber 19.

A transducer 20 is provided to measure the differential pressure betweenchambers 18 and 19. A transducer 21 measures the actual pressure withinthe test chamber 19. A further transducer 22 provides measurements ofatmospheric pressure. A tracking control device 25 receives pressureinformation from transducers 20 and 21 and adjusts supply valve 27 tomaintain substantially the same pressure in seal chamber 18 as withinthe remainder of the pipe forming the test chamber 19. As leakage fromthe test volume may occur due to a small imperfection in the pipe (suchas leakage at a joint or pinhole corrosion), this will cause a drop inpressure in chamber 19 and so chamber 18 pressure is automaticallyadjusted accordingly to prevent the risk of leakage over the sealingedge of the bag 15 if there is a differential pressure present.

Similarly, if there is leakage around the sealing edge of the bag 14,the differential pressure measurement will cause the tracking control toadjust the pressure from supply 27 via pipe 17. The supply regulatorwill have means to vent gas as well as supply it, in order to maintainthe required seal volume pressure.

If leakage is present in the test volume part of the pipe, the control25 will then track the test pressure as it falls and so the pressuredrop across the band of pressures can be used to give an accurateleakage versus pressure profile.

A data handling device shown as processor 26 will store information foranalysis. This can be configured using a portable computer.

The small changes in differential pressure as the control tracks thisand brings this back in to line will indicate the system is operatingcorrectly. No change could indicate a deflated bag 15.

In practice the test device 12 would be connected to an umbilical whichwould carry the supply pressure pipe as well as bag inflation supply andconnections for the transducers. The umbilical would typically passthrough a seal at the end remote from the test volume chamber.

A more detailed arrangement for the FIG. 1 configuration is shown inFIG. 2.

The test device 12 shows the bags 14 and 15 coupled via a spring element30 (e.g. helical spring) to allow flexibility during insertion takinginto account pipe bends. The bags when deflated will be less than thediameter of guide-piece 31 which may be a shaped plastic cap to assistin insertion. The cap is of a sufficient diameter to reduce damage riskto the following deflated bags. The umbilical 32 will be of reinforcedplastic and carries pneumatic sense and control lines (lines 1-5). Inpractice transducers 20 and 21 are provided outside the pipeline andhave small sensing lines attached.

A pressurized gas supply is received on line 41 and can be provided tothe pneumatic lines via regulators R1-R3. Switching the lines iseffected by solenoid valves V1-V4.

Line 1 is connected between the test volume and solenoid valves V3 andV4. It can be used to increase pressure in the test volume (at location37), up to a maximum pressure set by regulator R1, by opening valve V3,or as a path to a calibrated leak by opening valve V4. This latterfunction is required for test volume quantification.

Line 2 is a sense line connected between the test volume (termination36) and the absolute pressure transducer 21 to provide a referencesignal for the electro-pneumatic (EP) tracking regulator 40 set point. Atapping from this line connects to one side of the DP transducer 20.

Line 3 is a sense line connected between the seal volume (termination38) and the other side of the DP transducer 20. The DP transducermeasurement provides an error signal which can be used for fine tuningof the tracking controller 25 (configured as a portable computer withassociated screen 25 a).

Line 4 connects the outlet of the EP tracking regulator to the sealvolume so as to control the seal volume pressure (termination 39).

Line 5 allows the bag seals to be inflated or deflated by the opening ofnormally closed solenoid valves V1 or V2 respectively.

FIG. 3 shows the tracking control function illustrated schematically.The absolute test volume pressure from transducer 21 together with theatmospheric pressure from transducer 22 are subtracted in subtractor 41and filtered via filter 42. Following amplification in amplifier 45 itis received as the reference signal for the EP regulator set point. Thedifferential pressure measured by transducer 20 will be amplified andpasses as a feedback signal to subtractor 43 to cause it for the EPregulator pressure to be brought back on track if a differentialpressure is measured. Although the arrangement could be hardwired it isconvenient for this operating function to be under software control.

The invention has been described in relation to a single configurationfor use typically with small diameter service pipes. However it ispossible for the arrangement to be modified so as to be applicable tolarger, higher pressure gas pipes. In such a configuration two spaceddevices are arranged each with their own seal volume chamber anddefining therebetween the test volume chamber. This allows the devicesto seal each end of the test volume and ensures that leakage does notoccur from either end as the seal volume pressure will correspond tothat within the test volume and will track this should it fall due topipe imperfection.

The expanded configuration is shown in FIG. 4 and includes two testdevices 12 a and 12 b. They will each have associated circuitry as shownin the figure. The devices with associated umbilical can be insertedinto the pipeline via the camera launching tubes 50 and 51 of knownconstruction.

In an alternative configuration shown in FIG. 5, the structure takesadvantage of known iris valves 60, 61, 62 and 63. In this arrangementthe bags are inserted separately. However in combination with themeasurement transducers and the tracking control they provide a similarsealing and testing configuration to that of FIG. 4.

What is claimed is:
 1. A leak testing system for pipes including meansfor providing a temporary seal at a first location in a pipe; means forproviding a substantially equal pressure between the first location andan adjacent test location in the pipe to prevent fluid passagetherebetween; means for determining any pressure decay at the testlocation indicative of pipe leakage; and means for measuring andadjusting the pressure in the first location to track the pressure inthe test location so as to maintain the substantially equal pressurebetween the first and test locations during testing.
 2. A system asclaimed in claim 1 wherein the means for providing a temporary sealcomprise a first sealing member spaced from a second sealing member soas to define a first seal chamber with the inner pipe wall.
 3. A systemas claimed in claim 2 including third and fourth sealing members forlocation at a spaced position to provide a second seal chamber, the pipeportion between the first and second seal chambers comprising a testchamber.
 4. A system as claimed in claim 1 including atmosphericpressure sensor means for providing pressure information to assist indetermining leakage.
 5. A leak testing system for pipes comprising:means for providing a temporary seal at a first location in a pipe;means for providing a substantially equal pressure between the firstlocation and an adjacent test location in the pipe to prevent fluidpassage therebetween; means for determining any pressure decay at thetest location indicative of pipe leakage; and means for measuring andadjusting the pressure in the first location to track the pressure inthe test location so as to maintain the substantially equal pressurebetween the first and test locations during testing, wherein the meansfor providing a substantially equal pressure includes a source of fluidunder pressure, valve means for introducing fluid into the firstlocation and differential pressure detection means for determining whenthe pressure in the first and test locations are equal.
 6. A system asclaimed in claim 5 wherein the means for adjusting the pressure in thefirst location to track pressure decay includes means connected to thedifferential pressure detection means and control means to operate thevalve means to reduce pressure at the first location if the testlocation pressure falls.
 7. A system as claimed in claim 5 wherein themeans for providing a temporary seal includes first and second spacedinflatable bags providing the first location therebetween.
 8. A systemas claimed in claim 7 wherein umbilical means are provided connected tothe bags to allow remote inflation and pressure determination.
 9. Asystem as claimed in claim 7 wherein the first and second bags areresiliently coupled to allow passage through bends in the pipe andwherein protector means are provided to prevent damage to the bags whendeflated during passage through the pipe.
 10. A system as claimed inclaim 5 including an electronic control device for continuouslydetermining the pressure in the test location and the differentialpressure between the first and test locations, so as to continuouslycompensate for any pressure decay in the test location whilstcontinuously determining the absolute pressure in the test location. 11.A system as claimed in claim 10 including storage means for holdingparameter information.
 12. A system as claimed in claim 10 includingmeans for adjusting the absolute pressure information from the testlocation in dependence on measured atmospheric pressure, filter meansfor filtering the measured signals and means for providing an adjustedfluid pressure signal for pressure control to the first locationdependent on the measured signals.
 13. A system as claimed in claim 12including feedback means taking into account the differential pressuremeasurement.
 14. A method for testing leaks in pipes and comprising:providing a temporary seal at a first location in a pipe; providing asubstantially equal pressure between the first location and an adjacenttest location in the pipe to prevent fluid passage therebetween;determining any pressure decay at the test location indicative of pipeleakage; and measuring and adjusting the pressure in the first locationto track the pressure in the test location so as to maintain thesubstantially equal pressure between the first and test locations duringtesting.
 15. A method as claimed in claim 14 including providing a firstseal spaced from a second seal so as to define a first seal chamber withthe inner pipe wall.
 16. A method as claimed in claim 15 includingproviding a third and fourth seal located at a spaced position toprovide a second seal chamber, the pipe portion between the first andsecond seal chambers comprising a test chamber.
 17. A method for testingleaks in pipes comprising the steps of: providing a temporary seal at afirst location in a pipe; providing a substantially equal pressurebetween the first location and an adjacent test location in the pipe toprevent fluid passage therebetween; determining any pressure decay atthe test location indicative of pipe leakage; measuring and adjustingthe pressure in the first location to track the pressure in the testlocation so as to maintain the substantially equal pressure between thefirst and test locations during testing; providing a source of fluidunder pressure; introducing fluid into the first location; and detectingdifferential pressure to determine that the pressure in the first andtest locations is equal.
 18. A method as claimed in claim 14 includingmeasuring atmospheric pressure for providing pressure information toassist in determining leakage.
 19. A method as claimed in claim 17including continuously determining the pressure in the test location andthe differential pressure between the first and test locations so as tocontinuously compensate for any pressure decay in the test locationwhilst continuously determining the absolute pressure loss in the testlocation.